In recent years, consciousness of the environmental protection has been increasing, and importance of the solar photovoltaic power generation is more increasing. A solar battery cell is sandwiched by protective materials, sealed by a transparent resin, and then provided for use outdoors as a solar battery module. As the transparent resin for sealing, an ethylene-vinyl acetate copolymer (hereinafter sometimes abbreviated as “EVA”) or the like is used, and sealing is conducted by sandwiching the resin between the protective material and the solar battery cell, heat melting and then solidifying it. In order to efficiently arrange the solar battery cell and wiring it, it is preferable that plural solar battery cells are sealed within a single solar battery module.
Also, recently, the place at which a solar battery is set up is diversified, and the solar battery is used not only on the roof of a building but also at a wall portion. In the case of use at a wall, the solar battery is not only installed on an outer wall, but also it is employed to construct the wall itself by a solar battery module. At this time, if a space is provided among plural solar battery cells and the front and back surfaces of the solar battery are formed of a transparent material, it becomes possible to prepare a daylighting type solar battery module capable of taking light in the inside of the wall.
Japanese Utility Model Registration No. 2,500,974 describes a laminate composed of two plate-like bodies bonded via two adhesive sheets so as to sandwich a solar battery between the two adhesive sheets, wherein a sheet piece having a thickness substantially equal to the solar battery is sandwiched into a space formed between the adhesive sheets in the outside of the solar battery. It is described that according to such a construction, it is possible to make the thickness of the circumferential edge portion of the laminate uniform and to prevent peeling from occurring because the moisture hardly invades the foregoing space from the outside. It is described to use EVA as the adhesive sheet and to use a sheet glass for the plate-like bodies on the both surfaces.
JP-A-59-022978 describes a caulking adhesive sheet for solar battery module containing an ethylene-based copolymer and an organic peroxide, the both surfaces of which are provided with an embossed pattern. It is described that since the subject adhesive sheet has an embossed pattern, it can prevent blocking of the sheet from occurring and has excellent deaeration properties in the modulation stage, thereby hardly generating air bubbles. In the working examples of this patent document, there is described a lamination method in which the temperature is raised to 150° C. in the reduced pressure state in a vacuum laminator, the pressure reduction is continued at 150° C. for one hour, cooling is performed, and the pressure reduction is then stopped.
JP-A-09-036405 describes a laminated solar battery module prepared by putting a photovoltaic power element between a front face member and a back face member via a sealing resin to form a laminate, maintaining the laminate at a degree of vacuum of 5 Torr or lower for from 5 to 40 minutes, subjecting the laminate to thermocompression bonding at a degree of vacuum of 5 Torr or lower, and after the subject thermocompression bonding, cooling the laminate. It is described that by thermocompression bonding under such conditions, a module which hardly generates peeling of the surface member and hardly generates residual air bubbles is provided. It is also described that by inserting a non-woven fabric between the solar battery cell and the sealing material resin and releasing the air present in the laminate through gaps in the non-woven fabric, a problem of the generation of residual air bubbles can be improved.
JP-A-61-069179 describes a process of producing a solar battery panel including lamination process of deaerating a solar battery panel laminate composed of a solar battery cell laminated between a cover glass and a back face material via a filler by a double vacuum system, heating, then applying pressure, wherein EVA is used as the filler, and a double vacuum chamber is held at a specific temperature range for a specific period of time. It is described that by conducting the lamination under specific temperature conditions, the whole of EVA can be crosslinked without causing foaming and yellowing. According to the conditions described in the working examples thereof, when the temperature of the board surface in the heater side has reached 140° C., vacuum compression bonding is conducted, a crosslinking reaction is performed at 148° C., cooling is performed to 50° C. or lower, and the compression for bonding is then released.
However, in connecting plural cells to each other and sandwiching them between two panels, followed by performing thermocompression bonding and sealing, it was difficult to avoid breakage of the solar battery cells. In particular, in the case where the number of cells is large and the area of the entire module is large, a large load is likely non-uniformly applied, and the breakage of a part of cells which receive an excessive load was unavoidable. Since the plural cells are mutually connected in series within the module, if one cell is broken, a series of cells to be connected do not accomplish the function. In the case where the breakage of cell occurs, not only the appearance is impaired, but also a performance of power generation is largely lowered, and therefore, the product must be discarded as a defective. Accordingly, a sealing method which hardly causes the breakage of cell as far as possible is being demanded.
A first invention has been made for the purpose of solving such a problem and is aimed to provide a process of producing a solar battery module which, when plural solar battery cells are arranged and sealed by a transparent resin, can prevent breakage of the solar battery cells.
The foregoing prior patent document describes that the solar battery cells are sealed using an EVA sheet containing a crosslinking agent. And, according to the method described in the foregoing prior patent document, even when the temperature is raised to proceed with the crosslinking reaction, the laminate was placed under high vacuum, thereby continuing strong compression in the vertical direction by the atmospheric pressure.
However, at high temperatures at which the crosslinking reaction can proceed, the sealing resin becomes a liquid the viscosity of which has been lowered. Thus, when the laminate is strongly compressed in the vertical direction, there was a possibility that not only the resin is flowed out from the edge of the laminate, but also the solar battery cells move with the transfer of the resin. If the resin is flowed out, or the solar battery cells move, there was a possibility that not only the appearance is deteriorated, but also the wiring connected to the cells is broken, and therefore, improvements were desired. Nevertheless, if the lamination is performed without a pressure reduction operation, air bubbles likely remain in the product, leading to deterioration of the appearance, too.
A second invention has been made for the purpose of solving such a problem and is aimed to provide a process of producing a solar battery module having a good appearance, which can inhibit remaining of air bubbles, movement of solar battery cells, or flowing out of the sealing resin from the edge.